Implements AddStartupEventsForTelemetry() in startup_metric_utils.cc for in-coming startup telemetry

components/startup_metric_utils/browser/startup_metric_utils.cc

Index: components/startup_metric_utils/browser/startup_metric_utils.cc
diff --git a/components/startup_metric_utils/browser/startup_metric_utils.cc b/components/startup_metric_utils/browser/startup_metric_utils.cc
index 3f4144721d8c73ce73275ca3cc7232397f70ee1c..32acf5b39244ddc0b96b97f46f849e794c4a31f4 100644
--- a/components/startup_metric_utils/browser/startup_metric_utils.cc
+++ b/components/startup_metric_utils/browser/startup_metric_utils.cc
@@ -314,6 +314,8 @@ void RecordMainEntryTimeHistogram() {
           (browser_main_entry_time_raw_ms >> 1) & kLower31BitsMask);
 
   // A timestamp is a 64 bit value, yet histograms can only store 32 bits.
+  // TODO(gabadie): Once startup_with_url.* benchmarks are replaced by

[gab, 2015/11/12 14:41:38]

Please add bug#

[gabadie, 2015/11/12 17:43:34]

Done.

+  //    startup_with_url2.*, remove this dirty hack.
   LOCAL_HISTOGRAM_TIMES("Startup.BrowserMainEntryTimeAbsoluteHighWord",
       browser_main_entry_time_raw_ms_high_word);
   LOCAL_HISTOGRAM_TIMES("Startup.BrowserMainEntryTimeAbsoluteLowWord",
@@ -337,6 +339,20 @@ base::TimeTicks ExeMainEntryPointTicks() {
   return base::TimeTicks();
 }
 
+// Records "instant" trace events for global timings observed by telemetry.
+void AddStartupEventsForTelemetry() {
+  DCHECK(!g_process_creation_ticks.Get().is_null());
+  DCHECK(!g_main_entry_point_ticks.Get().is_null());
+
+  TRACE_EVENT_INSTANT_WITH_TIMESTAMP(
+      "startup", "Startup.BrowserProcessCreation", 0,
+      g_process_creation_ticks.Get().ToInternalValue());
+
+  TRACE_EVENT_INSTANT_WITH_TIMESTAMP(
+      "startup", "Startup.BrowserMainEntryPoint", 0,
+      g_main_entry_point_ticks.Get().ToInternalValue());
+}

[gab, 2015/11/12 14:41:38]

Also, FYI going forward, I think telemetry should care about more of the timings
in this file (which are mostly all more relevant than "main entry point" -- e.g.
first paint, etc.).

[gabadie, 2015/11/12 17:43:33]

Telemetry w'll use thoses values to diff to other instant events on its own side
for convenience, the reason why it is done this way.

+
 }  // namespace
 
 bool WasNonBrowserUIDisplayed() {
@@ -374,6 +390,7 @@ void RecordExeMainEntryPointTime(const base::Time& time) {
 
 void RecordBrowserMainMessageLoopStart(const base::TimeTicks& ticks,
                                        bool is_first_run) {
+  AddStartupEventsForTelemetry();
   RecordHardFaultHistogram(is_first_run);
   RecordMainEntryTimeHistogram();